Soviet Reactor Like Early U.s. Designs

May 4, 1986|By Rose Simmons of The Sentinel Staff

The graphite reactor used at the Soviet's Chernobyl nuclear power plant is based on early atomic energy designs and is more combustible than reactors used in most U.S. commercial units, industry experts say.

''Graphite is carbon like coal and it burns like coal, which accounts for the reports of fire at the Chernobyl plant,'' said Scott Peters, an energy analyst with the Atomic Industrial Forum, an industry association in Bethesda, Md.

A gravellike mineral, graphite is used to control the breakup of uranium atoms in the reactor.

The uranium is encased in metal alloy fuel rods. These rods are inserted in gaps throughout bricks of graphite in the reactor. About 30 tons of uranium are used in nuclear plants.

Another element, which naturally emits neutrons, also is inserted in the reactor. The neutrons bounce off the uranium and break loose the uranium atoms' neutrons, starting a chain reaction.

The breaking down of uranium atoms causes heat, which is picked up by water circulating through the reactor.

The water flowing through the reactor transfers this heat to water in the turbogenerator, causing it to boil and steam. The steam turns the generator, creating electricity.

Pressurized water reactors used in the United States, Canada and Europe operate on the same principle, but they use water to moderate the splitting of uranium atoms so that the process does not speed up and die out.

Without water or graphite to moderate the speed of the fission process, the uranium would split too quickly and die out.

Only 3 percent of uranium used for power generation is enriched or contains active neutrons, Peters said. The rest of the uranium is composed of non-radioactive material. By comparison, 90 percent of the uranium in an atomic bomb is enriched.

The United States built the first demonstration nuclear power plant in the world using graphite in 1942. Although the Department of Energy and the military later built several of these power plants, the commercial industry turned to the pressurized water reactors developed by the Navy in the 1950s, said Suzanne Phelps, a director in the nuclear division at Edison Electric Institute in Washington, D.C.

''Safety surely was one of the reasons,'' said Phelps. ''Graphite is burnable while water isn't.''